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Que
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THE ANTARCTIC
ENVIRONMENT
Climatic
Information
Knowledge of
Antarctica's climate is relatively recent, and
detailed, long-term studies did not really start
until the establishment of the first permanent
scientific research stations, and especially the
activities surrounding the International
Geophysical Year of 1957-58. Nowadays,
meteorological and related research is an
important part of the work - sometimes the main
work - of almost every station in the region and
data is accumulating rapidly.
The
main factors influencing the climate of Antarctica
are the waters of the Southern Ocean, the seasonal
variations of sea ice, the ice sheet that covers
the continent itself, and its high altitude and
high (southern) latitude. There are considerable
climatological differences between the sea, the
coastlines, and the interior. For instance, the
Southern Ocean has most clouds, followed by Lesser
Antarctica, while Greater Antarctica, with its
high, arid plateau, has the least cloud cover. The
key points to bear in mind are that Antarctica is
extremely cold, dry, and windy, with little
precipitation.
The Coldest
Continent
First, Antarctica is the
coldest continent. Mean temperatures in the
interior during the coldest month (August) range
from -40º to -70ºC (-40º to -94ºF) and in the
warmest month (February) range from -15º to -45ºC
(5º to -49ºF). The lowest outdoor temperature ever
recorded on earth is -89.6ºC (-129.3ºF), which was
recorded in 1983 at the Russian Vostok station on
the inland ice cap. At sea level, Antarctic
temperatures are some 10º-17ºC (50º-63ºF) colder
than the Arctic.Nevertheless, there are
considerable variations. At the sub-Antarctic
islands, for example, temperatures may range from
about -40ºC in midwinter (August) to +14ºC in
January or February (-40º to
+57ºF).
The
Windiest Continent
Antarctica is
also the windiest of the continents. Apart from
global wind currents, Antarctica actually creates
its own wind systems. Cold dense air essentially
slides from the high interior ice fields towards
the lower areas along the coasts. At the edges of
the ice plateau the winds accelerate, thereby
lifting and blowing clouds of snow high into the
air. The strongest winds are habitually found on
the long coastal slopes of Greater
Antarctica.
Some coastal areas endure
almost constant strong winds, whereas other areas
may be quite calm much of the time and then
suddenly experience hurricane force winds as air
rushes down through glacial valleys. These sudden
and unexpected winds are called katabatic, or down
slope, winds. The famous Australian explorer
Douglas Mawson established a base at Cape Denison,
Commonwealth Bay, in 1912 and recorded wind speeds
for two years. This is reputed to be the windiest
place on earth, because the average wind speed
during that period was 72 kilometers per hour (45
miles per hour), and gusts of more than 240 kph
(150 mph) were common. Nevertheless, wind speeds
have been observed to drop very significantly just
a few miles away from the
coast.
Visitors to Antarctica should
be aware that katabatic winds can occur quite
suddenly, and with little warning, but then die
down again just as quickly. They create
dramatically low effective temperatures, due to
the wind-chill factor. In the Southern Ocean,
strong gale-force winds are quite common,
especially in the region between 40º-60ºS. These
cyclonic storms are caused by extremely cold air
coming from Antarctica meeting the relatively warm
and moist air over more northerly seas. This
accounts for the fearsome reputation of the Drake
Passage. The storms tend to circle Antarctica from
west to east.
The Driest
Continent
Surprisingly, Antarctica
is the driest continent. By definition, most of
the continent is a desert. There is very little
precipitation each year in the interior, and the
vast amount of ice and snow which make up the
polar ice cap has accumulated over many millions
of years. The mean annual accumulation for the
entire continent amounts to less than five
centimeters (two inches) of water equivalent,
which is just slightly more than that of the
Sahara Desert.
But some coastal
areas, particularly the west side of the Antarctic
Peninsula, receive much more precipitation. The
tip of the peninsula receives about 90 centimeters
(35 inches) of water equivalent each year. Here
and in the South Shetland Islands it may rain,
sometimes quite heavily - a typical maritime
climate.
Despite what has been said
in this section, visitors to the Antarctic
Peninsula region need not expect to experience
very bad weather as a matter of course. Crossings
of the Southern Ocean can be quite easy and severe
storms are infrequent in the southern summer
months. The narrow waterways of the Antarctic
Peninsula are quite protected. Likewise, sunny
days are rather common in Greater Antarctica and
the sun even shines among the subantarctic islands
and Antarctic Peninsula . Although visitors should
be prepared for cold weather at any time, it is
surprising how often it can seem almost too warm
to wear a parka. The average summer temperature is
near freezing.
The Antarctic
Circle
It is interesting to
understand the significance of the Antarctic
Circle and its relation to the hours of daylight.
As you travel farther south in the austral summer
months, the days get progressively longer. The
Antarctic Circle is located at about 66º33'S (its
position varies very slightly from year to year,
as the earth wobbles about its axis). This circle
marks the northernmost point at which the sun is
visible for 24 hours a day at the summer solstice,
on December 21, when it is at its highest point
above the horizon.
Before that date,
the sun is still climbing toward its zenith, and
afterwards it is descending, so if you reach this
region before or after December 21, you would need
to sail farther south of the Antarctic Circle to
experience a 24-hour day. (Exactly the same - but
opposite - process occurs in the northern
hemisphere, of course, so that the relevant date
applicable to the Arctic Circle is June
21.)
Four
Different Poles
The South
Pole that is referred to in everyday
conversation is in fact the Geographical South
Pole, which is the southernmost end of the earth's
rotational axis (the earth rotates around a line,
or axis, drawn between the north and south
geographical poles). But there are three other
"poles" which are of interest to
scientists.
The Magnetic South
Pole is where the lines of force of the
earth's magnetic field converge. The position of
this pole is constantly moving, by some 10-20
kilometers per year, due to variations in the
earth's magnetic field. Ships' navigation officers
have to take into account this magnetic variation
when interpreting their compass readings. The
magnetic south pole is currently (1997) located
off Adélie Land, in the French sector of
Antarctica, in the general vicinity of the Dumont
d'Urville station.
The Geomagnetic
South Pole is a theoretical definition used to
rationalize variations in the earth's magnetic
field. It is located at latitude 78º05'S,
longitude 111ºE, in the Australian sector near the
Russian Vostok station.
The Pole
of Relative Inaccessibility is the center of
the continent as measured by its distance from the
coasts. It is located at latitude 82º06'S,
longitude 54º58'E, also in the Australian
sector.
Copyright © Nigel
Sitwell & Tom Ritchie / Quark / Terra Mater
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